Stacked annealing system

ABSTRACT

A process chamber includes an opening, two or more stacked cold plates adjacent the opening, two or more stacked hot plates adjacent the cold plates, and a rotatable wafer transport capable of moving a wafer between the cold plates and between the hot plates for processing of the wafer. The wafer can be rapidly heated while between the hot plates. The wafer transport has perpendicular walls about a pivot such that when the wafer is between the cold plates or between the hot plates, one of the walls separates the cold and hot portions, thereby increasing the efficiency of cooling and heating.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/144,359, filed Jun. 3, 2005, which is herein incorporated byreferences for all purposes.

BACKGROUND

1. Field of the Invention

The present invention relates generally to semiconductor waferprocessing systems, and more particularly to such systems for thetransfer of semiconductor wafers to a processing chamber.

2. Related Art

High temperature processing of silicon wafers is important formanufacturing modern microelectronics devices. Such processes, includingsilicide formation, implant anneals, oxidation, diffusion drive-in andchemical vapor deposition (CVD), may be performed at high temperaturesusing conventional thermal processing techniques. Furthermore, manymicroelectronics circuits require feature sizes smaller than one micronand junction depths less than a few hundred angstroms. In order to limitboth the lateral and downward diffusion of dopants, as well as toprovide a greater degree of control during processing, it is desirableto minimize the duration of high temperature processing.

Semiconductor wafers, flat panel displays, and other similar substratestypically have numerous material layers deposited thereon during devicefabrication. Some commonly deposited layers (e.g., spin-on glass (SOG)films) may contain contaminants, defects or undesirable microstructuresthat can be reduced or removed by heating or “annealing” the substrateat an appropriate temperature for an appropriate time. Other depositedlayers (e.g., copper films) may have properties that undesirably changeover time or “self-anneal”, resulting in unpredictable deposited layerproperties (e.g., unpredictable resistivity, stress, grain size, andhardness). As with contaminants, defects, and undesirablemicrostructures, deposited layer properties often can be stabilized by acontrolled annealing step. Following the annealing step, the substratepreferably is rapidly cooled to stop the annealing process, and so thatother processes can be performed on the substrate, in order to increasethroughput.

Conventionally, annealing is performed within a quartz furnace that mustbe slowly pre-heated, such as by lamps, to a desired annealingtemperature, or within a rapid thermal process (RTP) system that can berapidly heated to a desired annealing temperature. Unfortunately,conventional lamp-based RTP systems have considerable drawbacks withregard to uniform temperature distribution. One alternative tolamp-based RTP systems is to use a hot plate annealing to heat thewafer. Such systems are disclosed in commonly-owned U.S. Pat. Nos.6,809,035 and 6,345,150, both of which are incorporated by reference intheir entirety. These systems use a hot plate, which can be heated byheating elements on or adjacent to the plate or plates, positioned belowand/or above the wafer. The hot plate enables the wafer to be quicklybrought to a desired temperature, such as for annealing.

Thereafter, an annealed substrate is transferred to a separate coolingmodule that conventionally employs a cooled substrate support and isslightly backfilled with a gas such as helium to enhance thermalconduction. The separate cooling module increases equipment cost andcomplexity, as well as equipment footprint, and decreases substratethroughput by requiring undesirable substrate transfer time between theheating and cooling systems. Other conventional processing systems havea cooling mechanism within the same chamber as the hot plate, as opposedto in a separate module. Cooling down a heated chamber or heating up acooled chamber requires additional energy and time.

Accordingly, it is desirable to have a system capable of heating orcooling a wafer for RTP or other processes without disadvantages ofconventional systems, discussed above.

SUMMARY

According to one aspect of the present invention, a process chamberincludes at least two stacked cold plates and at least two adjacentstacked hot plates. A rotatable wafer transport pivots about a pointbetween the hot plates and the cold plates located near a side of theprocess chamber. The wafer transport comprises two walls connected tothe pivot point and perpendicular to each other and a wafer supportextending from at least one of the walls to support a wafer thereon. Thewafer support is positioned such that the wafer can be placed betweenthe two cold plates or the two hot plates for cooling or heating,respectively.

In one aspect of the invention, a wafer is inserted into the processchamber and onto the wafer transport, such as by a robot. The wafertransport is positioned such that the wafer is between two cold plates,with one of the transport walls separating the cold plates from the hotplates. Once a desired temperature is achieved, such as measured bythermocouples attached to the wafer transport, the wafer transport isrotated 90°. As a result, the wafer is moved from in between the coldplates to in between the hot plates and one of the walls of thetransport again separating the hot plates from the cold plates. Thewafer can then be rapidly heated by the hot plates to the desiredprocessing temperature. When processing is completed, the wafertransport is rotated back 90° to move the wafer between the two coldplates for cooling. The wafer can then be removed from the chamber orrotated back to the hot plates for additional processing.

The process chamber having two adjacently stacked cold and hot platescan be themselves stacked to create a low cost, simple verticalmulti-wafer processing system having a small footprint. In anotherembodiment, N stacked cold plates and N stacked hot plates can beadjacently placed into a single process chamber so that N−1 wafers canbe heated and cooled simultaneously, where N is greater than two.

Advantages of the present invention include more efficient cooling andheating of the wafer since the heating area and the cooling area withinthe process chamber are separated by walls on the wafer transport.Because the cool environment from the cold plates is not completely openwith the heated environment from the hot plates, it takes less time andenergy to heat and cool the wafer. Further, since the cooling mechanismis in the same process chamber as the heating mechanism, a simplerprocess chamber is possible.

These and other features and advantages of the present invention will bemore readily apparent from the detailed description of the preferredembodiments set forth below taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A and 1B show side and top views, respectively, of a processchamber according to one embodiment of the invention;

FIG. 2 is a side view of one of the walls of the wafer transport used inthe process chamber of FIGS. 1A and 1B according to one embodiment;

FIGS. 3A-3D are top views showing the operation of the process chamberof FIGS. 1A and 1B according to one embodiment;

FIG. 4 is a top view of a portion of a semiconductor wafer processingsystem according to one embodiment;

FIG. 5 is a flow chart showing one embodiment of the present inventionfor use with the process chamber of FIGS. 1-4;

FIG. 6 is a side view of a multi-wafer process system with stackedchambers according to one embodiment; and

FIG. 7 is a side view of a multi-wafer process system with stackedplates according to one embodiment.

Like element numbers in different figures represent the same or similarelements.

DETAILED DESCRIPTION

FIGS. 1A and 1B show side and top views, respectively, of a processchamber 100 according to one embodiment of the invention. Referring toFIG. 1A, chamber 100 includes two stacked cold plates 102 on one sideand two stacked hot plates 104 on the other side. A rotatable wafertransport 106 is rotatable about a pivot or axis 108 between cold plates102 and hot plates 104. Wafer transport 106 includes a wafer support 110for holding a wafer 112, where the wafer that can be rotated betweencold plates 102 and between hot plates 104. When wafer 112 is betweencold plates 102, the wafer is cooled. When wafer 112 is rotated betweenhot plates 104, the wafer is heated to a desired temperature, such asfor RTP or annealing. Chamber 100 includes an opening 114 to enable thewafer to be placed into and removed from chamber 100. Once the wafer iseither inserted or removed from the chamber, the opening can be sealed,as is known in the art with conventional mechanisms.

Opening 114 of chamber 100 may be a relatively small opening, but with awidth large enough to accommodate a wafer of between about 0.5 to 2 mmthick and up to 300 mm in diameter and enable a robot arm or other wafertransfer mechanism to enter and maneuver. In one embodiment, the heightof opening 114 is no greater than between about 15 mm and 40 mm,preferably, no greater than 20 mm. The relatively small opening sizehelps to reduce cold and/or heat loss from process chamber 100. Inaddition, the small opening size keeps down the number of particlesentering process chamber 100 and allows for easier maintenance of theisothermal temperature environment.

Referring now to FIG. 1B, wafer transport 106 includes perpendicularwalls 116 extending from axis 108. Opening 114 allows the wafer to beplaced onto wafer support 110, which in this embodiment is two parallelrods or beams 118 connected to arms 120 extending from one of walls 116.Other suitable wafer supports can also be used, such as a grid of thinintersecting beams with protruding pin supports to minimize the amountof contact on the wafer surface. One or more supports may include athermocouple or other temperature sensing device embedded therein tomonitor the temperature of the wafer. In one embodiment, the rods orbeams are made of a conductive or non-insulating material, which resultsin quicker heating and cooling of the wafer. Walls 116 extend to theedges of the chamber and are made of an insulating material in oneembodiment. Walls 116 are also short enough to fit between two hot orcold plates and may include multiple segments, such as segments betweenthe plates, above the plates, and below the plates.

FIG. 2 is a side view of showing one of walls 116 according to oneembodiment having three segments 200, 202, and 204 extending from axis108. The wafer is located on the wafer support attached to middlesegment 202. Lower segment 200 is located below the lower cold and hotplates, and the upper segment 204 is located above the upper cold andhot plates. Thus, the gaps between segments 200 and 202 and betweensegments 202 and 204 are such that the cold and hot plates are able torotate in and out between them.

FIGS. 3A-3D are top views showing the operation of process chamber 100according to one embodiment. Note that FIGS. 3A to 3D do not show thehot and cold plates for ease of illustration. In FIG. 3A, wafer 112 isinserted into chamber 100 and onto wafer support 110 through opening114. Wafer 112 can be loaded from a wafer container, such as a FrontOpening Unified Pod (FOUP), a loading station, or other suitablelocation or component. A robot or other transfer mechanism can be usedto retrieve the wafer and insert it onto wafer support 110. In thisposition, wafer 112 is located directly between the two cold plates.Depending on the temperature of the cold plates and the amount of timethe wafer is between the cold plates, wafer 112 can be cooled down to adesired temperature. Next, in FIG. 3B, wafer transport 106 is rotatedabout axis 108, such as with an external motor, to move wafer 112 awayfrom the cold plates and toward the hot plates. In FIG. 3C, wafertransport 106 has been rotated 90° so that wafer 112 is now completelybetween the two hot plates. Hot plates then heat wafer 112 to a desiredtemperature for processing. After processing, wafer transport 106 isrotated 90° back toward the cold plates. Once the wafer is cooled to adesired temperature, the wafer is removed from process chamber 100, asshown in FIG. 3D, or transferred back onto the hot plate for additionalprocessing.

Hot plate 104 may have a large mass relative to wafer 112 and may befabricated from a material, such as silicon carbide, quartz, inconel,aluminum, steel, or any other material that will not react at highprocessing temperatures with any ambient gases or with wafer 112. Hotplate 104 may be formed into any geometric shape, preferably a shapewhich resembles that of the wafer, e.g., a circular plate. In oneembodiment, the hot plate is circular with a radius slightly larger thanthe largest wafer to be processed, e.g., a 300 mm wafer.

Hot plate 104 can include heating elements to control the temperature ofthe hot plate. In one embodiment, at least one heat source is located ona periphery of hot plate 104. The heat source may be a resistive heatingelement or other conductive/radiant heat source, which can be made tocontact a peripheral portion of hot plate 104 or is embedded within hotplate 104. The resistive heating element may be made of any hightemperature rated material, such as a suitable resistively heatablewire, which is made from a high mass material for increased thermalresponse and high temperature stability, such as SiC, SiC coatedgraphite, graphite, AlCr, AlNi and other alloys. The temperature of hotplate 104 may be controllable to provide a variable temperaturedepending on the application, e.g., between about 50° C. and about 1500°C., preferably between about 100° C. and about 1200° C.

Cold plate 102 can be of similar shape as hot plate 104, i.e., circularwith a slightly larger diameter than the largest wafer. Cold plate 102may include individual cooling elements, such as electrical, liquid, orgas cooling components. For example, cold plate 102 can include aplurality of gas ports in the cold plate to provide a cooling gas to thewafer, where the cooling gas is supplied from an external gas source.The gas source can be tunable to selectively supply one or more gases tothe plurality of holes in the cold plate, where the amount of gassupplied to the cold plate is controlled by the controller based in parton the desired temperature of the wafer or cold plate.

As seen from FIGS. 3A, 3C, and 3D, when wafer 112 is between the coldplates (FIGS. 3A and 3D), wall 116 separates the cold plates and the hotplates, resulting in a more efficient cooling of the wafer since theamount of heat from the hot plates is kept away from the cold plates.Similarly, heating is also more efficient, since during heating (FIG.3C), wall 116 again separates the hot plates from the cold plates,thereby reducing the amount of cold entering the heating area. Wallsmade of a non-conductive material or insulating material helps keep thecold from the hot plate area and heat from the cold plate area.

In accordance with one embodiment of the invention, process chamber 100is an RTP chamber, such as those used in thermal anneals, dopantdiffusion, thermal oxidation, nitridation, chemical vapor deposition,and similar processes. Process chamber 100 has a small interior cavity.The small process chamber volume allows chamber 100 to be made smaller,and as a result, the overall system may be made more compact, requiringless clean room floor space. If a robot wafer loader, such as disclosedin U.S. Pat. No. 6,345,150, is used to transfer wafers into and out ofthe process chamber, multiple chambers can be vertically stacked, e.g.,directly over each other, to minimize floor space occupied by thesystem. Such a robot wafer loader can be moved up and down, rotated, andextended to retrieve wafers from a storage container, such as a FOUP,and transfer the wafer into the process chamber.

FIG. 4 is a top view of a portion of a semiconductor wafer processingsystem 400, which includes process chamber 100, FOUPs 402 and 404, and atransfer station 406. FOUP 402 or 404 can be accessed by a transportmechanism (not shown), which moves wafers from a FOUP to transferstation 406 or process chamber 100. The transport mechanism can be arobot that can be rotated and raised up and down with an extendable armto move the wafer to a desired destination. The operation and functionsperformed by a transport mechanism and FOUPs are generally well knownand understood by those of ordinary skill in the art. For example, thetransport mechanism may include a robot arm and an end-effector, each ofwhich may be made of a heat resistant material such as quartz, forpicking-up and placing wafers 112. The end-effector can be fixedlyattached to an attachment block on the end of the robot arm, whichaccepts a variety of end-effectors. For example, for a 3-axis robot, therobot arm can be made of multi-linkages capable of performing anS-motion or snake motion. The S-motion allows the robot to be positionedin a fixed location of process system 400, while the robot arm iscapable of accessing each module of the process system. For other typesof robots, such as a 4-axis robot, the S-motion is not needed. Thoseskilled in the art will realize appropriate constructions of robots,based on the type of robot. The transport mechanism may also function toflip wafer 112 before insertion into process chamber 100. This enablesboth sides of a wafer to be processed within the process chamber.

FIG. 5 is a flow chart showing one embodiment of the present inventionfor use with the process chamber of FIGS. 1-4. In operation 500, thewafer transport is rotated within the process chamber so that a firstone of the two arms of the wafer transport is parallel to a side wall(or perpendicular to the wall with the opening) and the second arm isbetween the hot plates and the cold plates. In this position, the wafercan be inserted onto the wafer transport, and the cold and hot zones areseparated from each other. Next, the wafer is inserted, such as from aFOUP, into the process chamber and onto the wafer support attached tothe wafer transport in operation 502. In this position, the wafer isbetween two cold plates, where it is cooled, as needed, in operation504. The wafer transport is then rotated, in operation 506, 90° so thatthe wafer is removed from the cold plates and moved between the two hotplates. After the 90° rotation, the first arm separates the cold platesand the hot plates, while the second arm is close to and parallel to theside wall. The wafer is then rapidly heated between the two hot platesin operation 508.

After the wafer has attained the desired temperature, the wafer isprocessed in operation 510. Next, in operation 512, the wafer transportis rotated back 90°, where the wafer is moved between the cold plates.If, as determined in operation 514, additional processing is required,the wafer transport is rotated 90° in operation 506 to place the waferbetween the hot plates for heating of the wafer in operation 508.However, if processing is complete, the wafer is removed from theprocess chamber in operation 516. Thus, the present invention enablesthe rapid thermal processing of a wafer using a simpler and smallersystem.

In another embodiment, process chamber 100 can be stacked, as shown inFIG. 6, to form a multi-wafer process system 600. While FIG. 6 showsjust two stacked chambers, any number of chambers can be stacked asdesired within system constraints. System 100 includes four cold plates602 and four hot plates 604, capable of processing two waferssimultaneously. Each process chamber 100 has its own opening forinserting and removing the wafer form the individual chambers.

FIG. 7 shows yet another embodiment in which more than two cold platesand more than two hot plates are stacked within a single process chamber700. Process chamber 700 is shown with six stacked cold plates 702 andsix stacked hot plates 704, capable of processing five wafers at a time.This embodiment enables wafers to be heated and cooled with less hot andcold plates than the system of FIG. 6. A single opening 706 allowswafers to be inserted and moved from chamber 700. Because of theincreased height of the chamber, the transport mechanism will have tohave a higher range of vertical motion in order to load wafers betweenany two adjacent cold plates 702.

Having thus described embodiments of the present invention, persons ofordinary skill in the art will recognize that changes may be made inform and detail without departing from the scope of the invention. Thusthe invention is limited only by the following claims.

1. A wafer annealing system, comprising: a process chamber having anopening for inserting and removing a wafer; a plurality of stacked hotplates; a plurality of stacked cold plates between the opening and thestacked hot plates; and a rotatable wafer transport having a pivotbetween the hot plates and the cold plates and a wafer support forholding the wafer, wherein the wafer transport is configured to rotatethe wafer between adjacent cold plates for cooling and between adjacenthot plates for heating.
 2. The system of claim 1, wherein the wafertransport further comprises a first wall extending from the pivot and asecond wall extending from the pivot, wherein the first and second wallsform a 90° angle from the pivot.
 3. The system of claim 2, wherein thewafer support is coupled to the first wall.